Heretofore, polyvinylchloride resin (a.k.a. PVC) has been commonly used as a base resin for resin compositions containing mineral filler, due to its ability to accept higher levels of such filler. For example, compositions comprising PVC and a mineral filler such as SiO.sub.2, BaSO.sub.4, and CaCO.sub.3 has been used in floor tile and sheeting applications, due to the high impact strength, abrasion resistance and flexibility of PVC, coupled with the lost cost associated with increased filler loadings.
However, PVC has come under increased scrutiny for several reasons. For example, the presence of chloride atom in the backbone structure of PVC renders it difficult to re-melt, re-extrude, and recycle, and leads to poor heat stability. In addition, when combusted, PVC tends to disadvantageously release noxious substances, such as hydrochloric acid. Further, PVC typically contains a plasticizer to improve flexibility, which plasticizer may leach from landfilled PVC and cause soil and/or water pollution. PVC is further disadvantageous in that it is thermally sensitive, and thus requires tighter temperature control in molding processes than non-halogen containing polymers.
In view of the above deficiencies, industry would find advantage in a halogen-free PVC replacement which is more easily recyclable, but which does not sacrifice physical properties.
U.S. Pat. No. 4,847,317 (Dokurno et al.) discloses filled thermoplastic compositions comprising: (a) 30-90 parts ethylene polymer, (b) 10-70 parts graft modified ethylene polymer, and (c) 20-70 weight percent filler, based upon the amount of (a) and (b). Those in industry would find advantage in compositions which tolerate filler levels greater than 70 weight percent. Those in industry would further find advantage in compositions which achieve the desired performance, but which utilize less than 10 weight percent functionalized polyethylene, more preferably less than 3 weight percent functionalized polyethylene.
U.S. Pat. No. 4,379,190 (Schenck I) teaches filled thermoplastic compositions comprising: (a) 5-60 weight percent of a mixture of at least two copolymers of ethylene, having specified polar comonomer contents, (b) 40-90 weight percent filler, and (c) 0-15 weight percent plasticizer. When the filler is present in an amount exceeding 75 weight percent, Schenck requires that the plasticizer be present in an amount of at least 1 weight percent, with plasticizer levels between 3 and 10 weight percent being preferred, and with plasticizer levels between 4 and 8 weight percent being most preferred.
U.S. Pat. No. 4,403,007 (Coughlin) describes filled thermoplastic composition comprising: 5-55 weight percent of a copolymer of ethylene with a functionalized comonomer, 1-15 weight percent plasticizer, and 40-90 weight percent filler.
U.S. Pat. No. 4,438,228 (Schenck II) discloses a filled thermoplastic composition useful, e.g., as sound-deadening sheeting for automotive carpet, comprising: (a) 5-55 weight percent of an ethylene/a-olefin copolymer, (b) 2-12 weight percent plasticizer, and (c) 40-90 weight percent filler.
PCT Publication WO 96/04419 discloses the use of substantially linear ethylene polymers in sheet materials for flooring. While the PCT Publication recognizes the potential use of substantially linear ethylene polymers in sheet materials comprising up to 85 weight percent filler, it does not utilize greater than 65 weight percent filler in the Examples.
In contrast to the teaching of Schenck I, Schenck II, and Coughline, those in industry would further find advantage in a filled plasticizer-free thermoplastic composition, i.e., a thermoplastic composition containing less than 3 weight percent, especially less than 1 weight percent plasticizer.
However, the compositions of above references do not teach or disclose substantially halogen-free, highly filled, plasticizer-free polyethylene-based compositions achieving high flexibility.